By Andrew Osborn
LONDON (Reuters) - Britain's opposition Labour Party said on Friday it would ensure cheaper energy costs for consumers by the end of this year if it wins a national election on May 7, promising it would immediately empower the energy regulator to force prices down.
Labour, which has floated the idea before but not previously spoken of timing, said it would enact legislation to give energy regulator Ofgem the power to force firms to cut prices as one of its first acts of government if elected.
"We will make sure that the regulator has that power, that duty, to ensure that prices comes come into effect this winter," Caroline Flint, the party's energy spokeswoman, told BBC radio.
"Wholesale costs have fallen on average by about 20 percent over the last 15 months and that hasn't been passed onto bill payers."
Labour in 2013 promised to freeze gas and electricity prices for 20 months if it won power, securing a temporary lift in opinion polls. It was criticised by the country's big six energy suppliers and business groups at the time.
Level or narrowly just behind or ahead of Prime Minister David Cameron's Conservatives in opinion polls, Labour has tried in the past to blame Cameron for inflicting what it calls a cost of living crisis on Britain.
Many voters have felt their living standards squeezed by inflation outstripping wages until recently. But cheaper oil has handed Cameron a political gift by lowering prices for everything from petrol to food, blunting what was meant to be Labour's main attack line.
The Conservatives and many energy firms oppose Labour's move to give Ofgem extra powers, saying it amounts to meddling in the free market. They argue Labour's earlier price freeze threat has discouraged firms from lowering prices as they hedge their bets.
Flint said she did not accept that, saying intervention was the only way forward.
"We always have 101 reasons from the energy companies and those in the sector about why they can't pass on wholesale costs," she said. "We've seen recently that actually they have started to pass on some of those costs, but it's only between 1 and 5 percent and it's on gas alone not electricity."
Given that costs had fallen by an average 20 percent, she said it didn't add up.
"I think it's fair to say that's something not right here," said Flint.
Britain's largest energy suppliers, including Centrica's British Gas and SSE , have announced gas tariff reductions between 1.3-5.1 percent this year, arguing they were passing on the highest possible savings.